MFC 327737:
USNO and possibly others have misinterpreted the maining of the
leapseconds last-update field and incorrectly increment it when changing
the file even though the leapsecond data has not changed. For instance,
if a leapsecond file is obtained from USNO, when it expires it will not
be replaced by a newer file from other sources because it has an
incorrect later last-update (version).
This corrects r304780.
PR: 225029
Submitted by: ian
git-svn-id: svn://svn.freebsd.org/base/stable/10@327859
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